Characterization of spray and combustion processes of biodiesel fuel injected by diesel engine common rail system

The influence of injection pressure up to ultra-high value of 300 MPa, nozzle hole diameters of 0.16 and 0.08 mm and fuel properties such as boiling point, cetane number and oxygen content on spray, ignition and combustion characteristics of biodiesel fuel in diesel engine were investigated. Biodiesel from palm oil source (BDF) and for comparison the JIS #2 diesel fuel were utilized. The Mie-scattering technique was used for characterizing the evaporating spray formation processes while the OH chemiluminescence technique was used to determine the ignition and the lift-off length of the combusting flame. Furthermore, the two color pyrometry was applied to study the soot formation processes. The results obtained indicated that due to higher boiling point, the BDF produced longer liquid phase length as compared to diesel. It was observed that the ignition region was larger for the 0.16 mm nozzle as compared to the 0.08 mm. Due to the enhanced mixing processes, ignition delay decreased as the injection pressure increased from 100 to 300 MPa respectively and also by reducing the nozzle hole diameter to 0.08 mm. Higher cetane number and oxygen content of the BDF facilitated shorter ignition delay as compared to diesel. The percentage stoichiometry air entrained increased by decreasing the nozzle hole diameter. The BDF flame produced shorter lift-off length and lower percentage stoichiometry air. Under higher injection pressures and decreasing nozzle diameter, the BDF produced less soot as compared to diesel. The fuel oxygen content in the biodiesel fuel played a greater role in the soot formation processes.